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Box 7.2 Implementing a New Worlds Science Plan • Carry out a focused program of computation and theory to understand the architectures of planets and disks. • Use the Kepler transit survey to measure the probability that a solar‐type star has a massive terrestrial companion, and that a red star harbors an Earth‐like planet. • Perform a microlensing survey from space using the recommended WFIRST to characterize in detail the statistical properties of habitable terrestrial planets. • Improve radial velocity measurements on existing ground‐based telescopes to discover planets within a few times the mass of Earth as potential targets for future space‐based direct‐detection missions. • Use ground‐based telescopes, including ALMA , AO‐equipped optical/infrared telescopes such as GSMT, and mid‐infrared interferometry, or space‐based Explorers, to characterize the dust environment around stars like the Sun, so as to gauge the ability of future missions to directly detect Earth‐size planets in orbits like that of our own Earth. • Locate the prime targets for hosting habitable, terrestrial planets among our closest stellar neighbors. • Use JWST to characterize the atmospheric or surface composition of planets within a few times the size of Earth, orbiting the coolest red stars. These are the planets that might be discovered by ground‐ and possibly space‐based surveys. • Follow up nearby systems discovered by Kepler. • Assess habitability by using IXO to characterize the frequency and intensity of flares on host stars. • Use ALMA and CCAT to seek biogenic molecules thought to be precursors to life. • Develop the technology for an ambitious space mission to study nearby Earth‐like planets. The Physics of the Universe: Understanding Scientific Principles Astronomy has made many contributions to our understanding of basic physics and chemistry, ranging from Newton’s laws of gravitation to the discovery of helium, from providing much of the impetus for understanding nuclear physics to discovering new types of molecules unique to interstellar environments. Perhaps the best developed recent example has come from high-precision tests of the theory of gravity encompassed by Einstein’s theory of general relativity. However, these tests have been restricted to the situations where gravity is weak, and the strong field expression of the theory still remains to be tested. The discovery of dark energy and dark matter and the amassed evidence that is at least consistent with the predictions of the theory of inflation present two more examples where carefully controlled astronomical measurements contribute to current understanding of fundamental physics. Here the committee highlights these three topics, mindful of a range of other such opportunities, mentioned below. The standard model of cosmology developed in the 1980s and 1990s has been amply confirmed over the past decade by observations of the cosmic microwave background (CMB) using ultrasensitive radio telescopes on the ground, balloons, and spacecraft. Using a combination of these and other observations, astrophysicists have shown that the geometry of space is approximately flat, that the age of the universe is 13.7 billion years, and that there is nearly five times as much matter in a dark, invisible form as in normal matter that can turn into visible stars. The past decade also saw strong affirmation of the remarkable discovery that the expansion of the universe is accelerating. We can now say that there is a ubiquitous and ethereal substance called “dark energy” that is expanding the fabric of space between the galaxies at ever faster speeds and accounts for 75 percent of the mass-energy of the universe today. The effects are so tiny on the scale of an experiment on Earth that the only way forward is to use the universe at large as a giant laboratory. Two complementary approaches to understanding dark energy have been considered by this survey: one on the ground and the other in space. On the ground, the proposed LSST would provide PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 7-10
optical imaging of brighter galaxies over half the sky every few days. It would build up measurements of galaxy images that are distorted by (weak) gravitational lensing and detect many relatively nearby supernovas. From space, the proposed WFIRST would produce near-infrared images of fainter galaxies over smaller areas and observe distant supernovas. It would also provide near-infrared spectroscopy for sensitive baryon acoustic oscillation measurements. What has become clear over the past few years is that instead of just considering dark energy in different regimes, LSST and WFIRST will actually be quite synergistic, and observations from one are essential to interpreting the results of the other. In particular, by working together, they would provide the powerful color information needed for redshift 10 estimation. The properties of dark energy would be inferred from the measurement of both its effects on the expansion rate and its effects on the growth of structure (the pattern of galaxies and galaxy clusters in the universe). In doing so it should be possible to measure deviations from a cosmological constant 11 larger than about a percent. Massively multiplexed spectrographs in intermediate-class and large-aperture ground-based telescopes would also play an important role. Second, and most remarkably, it is now possible to contemplate observing the earliest moments of the universe. Another source of gravitational radiation may be the most intriguing of all. The patterns in the CMB are theoretically consistent with what could have been laid down during the first instants after the big bang during an epoch of rapid expansion, called inflation. The recently launched Planck satellite will produce higher-resolution, all-sky CMB temperature and polarization maps at many frequencies. Complementary observations from the ground will look at patches of the sky with fine angular resolution. These experiments will be able to compare the temperature fluctuations on a range of scales, from those so small that they will grow into only a small group of galaxies today, to the largest-scale fluctuations observable on the whole sky, which will allow scientists to see if the fluctuations are truly random or instead non-Gaussian, as some theories suggest. However, the most ambitious goal of all is to try to detect a particular pattern in the polarization—called B-modes—that is caused by very long wavelength gravitational radiation that would be created at the time of inflation. The B-modes are a window allowing us to peer far back beyond the screen of the CMB into the period of inflation. The convincing detection of B-mode polarization in the CMB produced in the epoch of reionization would represent a watershed discovery. The strength of the associated fluctuations, now constrained to less than 20 percent, should be measurable by upcoming telescopes at a level as low as 20 times weaker than the current limit. If these fingerprints of inflation are detected, then a decadal survey independent advice committee (as discussed in Chapter 3) could determine whether a technology development program should be initiated with a view to flying a space microwave background mission during the following decade that would be capable of improving the accuracy by a further factor of 10 and elucidating the physical conditions at the end of inflation. Third, an inescapable consequence of general relativity is the existence of black holes. Once mere conjectures, black holes are now known to be very common. They are found at the centers of normal galaxies like our own Milky Way and as companions to normal stars transferring mass to their neighbors through winds. Gas close to a black hole radiates X-rays prodigiously and offers a quantitative observational test of relativistic theory that would be possible to conduct with the proposed sensitive International X-ray Observatory IXO. Another general property of black holes is that they create jets of hot plasmas that move at speeds very close to that of light and create intense beams of radiation from the longest radio wavelengths to the highest gamma-ray energies. The proposed Advanced Čerenkov Telescope Array (ACTA) will use high-energy gamma-ray observations to probe the properties of black holes. 12 10 Spectral lines in the electromagnetic radiation emitted by an object are shifted to longer (“redder”) wavelengths if the object is moving away from an observer. The greater the redshift, the more distant the object. 11 A term in Einstein’s general relativity theory that represents the density and pressure associated with empty space, which counteracts the gravitational pull of matter. 12 The committee also considered a proposed black hole finder mission called the Energetic X-ray Imaging Survey Telescope (EXIST). This was recommended by AANM and further considered by the NRC’s Beyond PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 7-11
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THE NATIONAL ACADEMIES PRESS 500 Fi
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COMMITTEE FOR A DECADAL SURVEY OF A
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Panel on Stars and Stellar Evolutio
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DOUGLAS FINKBEINER, Harvard Univers
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SPACE STUDIES BOARD CHARLES F. KENN
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activities 2 that have emerged from
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In addition to the 27 panel meeting
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Acknowledgment of Reviewers This re
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The Accelerating Universe 2-26 The
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APPENDIXES A Summary of Science Fro
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light up the universe, marking the
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RECOMMENDED PROGRAM Maintaining a b
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TABLE ES.4 Space: Recommended Activ
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Cosmic Dawn: Searching for the Firs
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this imprint would both probe funda
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important outcome will be to open u
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estimated to be on the order of $20
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observatories. For NASA an annual b
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surveys of large fields, enabling s
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RECOMMENDATION: U.S. investors in a
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departments and the community as a
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dominate spending; (2) private-publ
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us was certainly evident during the
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BOX 2-1 Other Worlds Around Other S
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FIGURE 2‐2 The source 3C 75, show
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FIGURE 2‐3 Numerical simulation o
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FIGURE 2‐4 Left panel: Image of t
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FIGURE 2‐6 Top: Schematic of the
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Most stars with masses smaller than
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BOX 2-2 The Origin of Planets After
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send material raining into the cent
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BOX 2-4 Lifecycles in Galaxies One
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Stars Stars are the most observable
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ubiquitous high-energy charged-part
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The Nature of Inflation As describe
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FIGURE 2‐11 Pie chart showing the
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An important clue to the nature of
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Studying the properties of neutron
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FIGURE 2‐14 A possible pathway is
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partners and makes recommendations
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As astronomy research has blossomed
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are increasingly relevant. The Euro
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TABLE 3-1 Currently Operating OIR F
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29% 1990 44% US Priv US Fed Other E
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CONCLUSION: Complex and high-cost f
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Space Observatories The Laser Inter
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Physics Division (PHY); the Mathema
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4 Astronomy in Society Astronomy of
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FIGURE 4‐2 The dust sculptures of
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FIGURE 4‐5 President Obama takes
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Astronomy Inspires in the Classroom
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teaching the scientific method. The
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where the fraction of astronomers h
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Percentage of AAS Membership by Fie
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0.4 0.3 0.2 0.1 PL SO IM AG SF IN S
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FIGURE 4‐12 Number (top panel) an
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Page 121: assistant and associate professor p
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Page 126 and 127: THEORY Emerging Trends in Theoretic
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Page 130 and 131: TABLE 5‐2 Support for astrophysic
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Page 134 and 135: FIGURE 5‐7 Highly cited HST publi
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Page 138 and 139: FIGURE 5‐8 Number of PhDs per yea
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Page 154 and 155: TOWARD FUTURE PROJECTS, MISSIONS, A
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Page 163 and 164: FIGURE 7.1 Survey time line showing
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Page 167 and 168: Box 7.1 Implementing a Cosmic Dawn
Page 169: JWST, with its superb mid-infrared
Page 173 and 174: Box 7.3 Implementing the Physics of
Page 175 and 176: FIGURE 7.2 Multiwavelength images o
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Page 179 and 180: FIGURE 7.4 Science accomplishments
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Page 187 and 188: Laboratory Astrophysics As describe
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Page 193 and 194: excel at high spectral and spatial
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Page 207 and 208: A Summary of Science Frontiers Pane
Page 209 and 210: PLANETARY SYSTEMS AND STAR FORMATIO
Page 211 and 212: A preliminary recommended program w
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decadal research strategy with reco
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CFP CHIPSat CIP CGRO CMB CMU CoBRA
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NRC NSB NSF NSF-AGS NSF-ARC NSF-AST
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